We wanted to make Gin/Tonic this weekend but was surprised... no tonic water in the shops. Finally managed to buy some 0.5 l at Coop, but culd not found any big bottle...
Kind of obvious, but anyway: Look at a drinks shop, for example a branch of "Rio Getränke"... they have one liter pet bottles. I do not know the Western Swiss equivalent...
Plenty of Schweppes products in Coop. Also as others have said the big bottles of Schweppes tonic are available in Denner. Be warned though that I don't think the Swiss can be big tonic drinkers since the stuff seems to be priced at Johnny 'banker' foreigner prices i.e. the tonic water costs far more than beer.
As far as the light or diet version of the products goes I've never seen them in Switzerland.
The margin on the stuff here is such that several times a year they sell it at about a third off. That is the time to stock up.
How exactly? I mean, soda water is just water with bubbles, and bubbly "mineral" water is just water with bubbles. I'm not quite sure that I follow what the difference is.